Detailed Description
The invention provides a method for preparing battery-grade iron phosphate by using pyrite cinder, which comprises the following steps:
(1) acid leaching of pyrite cinder: taking pyrite cinder as an iron source, and sequentially performing a pulping process, a primary acid leaching process and a secondary acid leaching process to obtain an iron-containing leaching solution;
(2) removing impurities from the iron-containing leachate: sequentially carrying out a reduction process, an aluminum removal process and a heavy metal removal process on the iron-containing leachate to obtain a ferrous sulfate solution;
(3) synthesizing iron phosphate: and reacting the ferrous sulfate solution with a phosphate solution to obtain the iron phosphate.
Specifically, the overall process flow is as follows:
the whole process flow is as follows:
and (1) acid leaching the pyrite cinder. And (3) taking the pyrite cinder which is a byproduct in the acid preparation from the pyrite as an iron source, and sequentially performing a pulping process, a primary acid leaching process and a secondary acid leaching process to obtain an iron-containing leaching solution.
First, the analysis of the main impurity elements of the pyrite cinder is shown in the following table 1:
TABLE 1
A pulping process. Adding concentrated sulfuric acid solution with the concentration of 90-99 wt%, preferably 98 wt% into the pyrite cinder, and uniformly mixing to obtain mixed slurry. Wherein the acid-solid weight ratio is controlled as follows: (1-5): 1, preferably (1-3): 1, the dripping time of the concentrated sulfuric acid solution is controlled to be 10-120min, preferably 30-90min, and the stirring can be continued for 20-60 min after the addition is finished.
② a primary acid leaching process. And adding pure water and a cosolvent EDTA into the mixed slurry, and uniformly mixing to obtain a primary acid leaching solution.
Wherein, the acid concentration in the primary acid leaching solution is controlled to be 20 wt% -85 wt%, preferably 45-70 wt%, the primary acid leaching solution is heated to 60-100 ℃, preferably 80-100 ℃, the reaction is carried out under stirring, the stirring intensity is preferably 250-350rpm, more preferably 300rpm, and the reaction time is 1-7h, preferably 2-3 h; wherein the addition amount of the cosolvent is 3-8% of the mass of the pyrite cinder.
In the present invention, all the stirring strengths are not particularly limited as long as uniform stirring is possible.
And a secondary acid leaching process. The secondary acid leaching process comprises the following steps: adding pure water into the primary acid leaching solution to control the acid concentration to be 30-45 wt%, the reaction time to be 0.5-2.5h, preferably 1-2h, the reaction temperature and the stirring intensity are in the same stage acid leaching process, and filtering to obtain the iron-containing leaching solution.
The reason for controlling the acid concentration of the reaction system is that the detection of the concentration of iron ions is inconvenient, so the control of the acid concentration controls the concentration of iron ions in the solution, and at the same time, the control also plays a role in reducing the viscosity of the solution, thereby increasing the moving speed of ions in the reaction and reducing the concentration of products to promote the forward progress of the reaction, and the concrete operations are as follows: adding pure water or filtering slag washing water after secondary acid leaching into the reaction solution to control the concentration of acid added into the system to be 30-45 wt%, and the reaction time to be 0.5-2.5h, preferably 1-2h, and then filtering to obtain iron-containing leachate; sampling to measure the content of the ferric iron.
Preferably, the secondary acid leaching step may further include: washing the leached residues after filtration, and reusing the washed washing water instead of pure water in the secondary acid leaching procedure for adjusting the acid concentration; the recycling aims to improve the recovery rate of the pyrite cinder iron.
And (2) removing impurities from the iron-containing leachate. And sequentially carrying out a reduction process, an aluminum removal process and a heavy metal removal process on the iron-containing leachate to obtain a ferrous sulfate solution.
A reduction step. The reduction process comprises: adding a reducing agent into the iron-containing leaching solution, reacting under stirring, and adding Fe in the solution 3+ Reduction to Fe 2+ Obtaining a crude ferrous sulfate solution;
wherein the reducing agent is one or more of sodium sulfite, sodium thiosulfate, sodium iodide and iron powder; the dosage of the reducing agent is 1.05 to 1.5 times of the stoichiometric ratio, preferably 1.1 to 1.3 times; the reaction temperature is normal temperature, the stirring intensity is preferably 250-350rpm, more preferably 300rpm, and the reaction time is 10-30 min.
Taking sodium sulfite as an example of the reducing agent, the main reaction equation generated in the reduction process is as follows:
2Fe 3+ +SO 3 2- +H 2 O=2Fe 2+ +2H + +SO 4 2-
aluminum removing process: adding a pH regulator into the crude ferrous sulfate solution under stirring, regulating the pH of the solution to 3.5-5.5, preferably 4.5-5.5, completely converting trivalent aluminum ions in the solution into aluminum hydroxide precipitate, continuously stirring for 20-60 min after regulating the pH, and filtering to obtain a solution after removing aluminum;
wherein the pH regulator is one or more of sodium hydroxide, ammonia water, sodium carbonate and sodium bicarbonate, the reaction temperature is normal temperature, and the stirring intensity is preferably 250-350rpm, more preferably 300 rpm.
The main reaction equation occurring during the aluminum removal process is as follows:
Al 3+ +3OH - =Al(OH) 3 ↓
and thirdly, heavy metal removing process. Adding a heavy metal trapping agent into the solution after aluminum removal for reaction for 40-90min at 40-60 ℃ under stirring, and then filtering to obtain a pure ferrous sulfate solution;
wherein the heavy metal capture agent comprises one or more of sodium sulfide, potassium sulfide and ammonium sulfide, and the stirring speed is preferably controlled at 350-450rpm, more preferably 400 rpm; the addition amount of the heavy metal scavenger is controlled to be 0.05-1g/L, preferably 0.1-0.7 g/L.
Adjusting the iron concentration. Preferably, the step (2) further comprises: a step of adjusting the iron concentration subsequent to the step of removing heavy metals, the step of adjusting the iron concentration comprising: adding pure water into the ferrous sulfate solution for dilution, and controlling the concentration of the ferrous sulfate in the solution to be 230-kg, preferably 220-kg, of 180-kg, so as to obtain a ferrous sulfate reaction solution for later use.
Synthesizing iron phosphate: and reacting the ferrous sulfate solution with a phosphate solution to obtain the iron phosphate.
The method for synthesizing iron phosphate in the present invention is not particularly limited, and a conventional production method may be employed.
In the invention, industrial phosphoric acid is taken as an example to synthesize the iron phosphate. Specifically, adding sodium hydroxide into phosphoric acid, and adjusting the pH of the solution to 7.0, wherein the oxidant is 20-30 wt% of hydrogen peroxide, and the addition amount of the hydrogen peroxide is 1.13-1.2 times of the reaction amount; adding hydrogen peroxide into a phosphorus salt solution with the pH value of 7.0, and uniformly mixing to obtain a reaction phosphorus salt solution for later use.
During synthesis, the reaction is controlled by the formula (n), (P): and (n), (Fe) ((1-1.05): 1) adding the prepared reaction phosphate solution into the ferrous sulfate solution dropwise by using the ferrous sulfate reaction solution as a base solution, heating to 88-96 ℃ after the dropwise addition is finished, reacting for 1-3h, filtering to obtain an iron phosphate filter cake, washing, drying and calcining the iron phosphate filter cake to obtain the battery-grade anhydrous iron phosphate.
Finally, from the viewpoint of effective utilization of resources and energy conservation and environmental protection, post-treatment can be performed on the iron phosphate mother liquor (the main components are sodium sulfate and EDTA) obtained after filtration, and the post-treatment comprises the following steps: evaporating, concentrating and cooling and crystallizing.
Introducing the iron phosphate mother liquor into mVR for concentration until the solution density is 1.17-1.2g/mL, then injecting the concentrated solution into a crystallization kettle for cooling crystallization, changing sodium sulfate in the solution into sodium sulfate decahydrate crystals for precipitation through cooling crystallization, and centrifuging through a centrifuge to obtain crystallization mother liquor and sodium sulfate decahydrate crystals, wherein the main component of the crystallization mother liquor is a solution containing EDTA, and the crystallization mother liquor can be reused as a cosolvent for the primary acid leaching process; because EDTA is lost in the whole process, when EDTA is reused for leaching again, the leaching rate can reach more than 96% by only supplementing 1-2% of EDTA. In addition, sodium sulfate decahydrate may be sold as a by-product. Thus, the full and effective utilization of resources is completed.
The present invention will be described more specifically by way of examples with reference to FIG. 1.
Example 1
This example illustrates the method for preparing battery-grade iron phosphate from pyrite cinder according to the present invention.
The pyrite cinder used in this example is obtained from pyrite cinder from auspicious cloud group, and the iron content and impurity element analysis thereof are shown in table 2 below:
TABLE 2
(1) Acid leaching of pyrite cinder:
a pulping process. Adding a concentrated sulfuric acid solution with the concentration of 98 wt% into the pyrite cinder, and uniformly mixing to obtain a mixed slurry. Wherein the acid-solid weight ratio is controlled to be 1.7:1, the dripping time of the concentrated sulfuric acid solution is controlled to be 60min, and the stirring can be continued for 20min after the dripping is finished.
② a primary acid leaching process. And adding pure water and a cosolvent EDTA into the mixed slurry, and uniformly mixing to obtain a primary acid leaching solution.
Wherein the acid concentration in the primary acid leaching solution is controlled to be 50 wt%, the primary acid leaching solution is heated to 98 ℃ and reacts under stirring, and the reaction time is 3 hours; wherein the addition amount of the cosolvent is 3 percent of the mass of the pyrite cinder.
And a secondary acid leaching process. The secondary acid leaching process comprises the following steps: adding pure water into the primary acid leaching solution to control the acid concentration to be 40 wt%, reacting for 1h, and filtering to obtain the iron-containing leaching solution.
(2) Removing impurities from the iron-containing leachate:
a reduction step. The reduction process comprises: adding sodium sulfite reducing agent into the iron-containing leachate, reacting under stirring, and adding Fe in the solution 3+ Reduction to Fe 2+ Obtaining a crude ferrous sulfate solution; wherein the dosage of the reducing agent is 1.1 times of the stoichiometric ratio; the reaction temperature was normal temperature, the stirring intensity was 300rpm, and the reaction time was 30 min.
Aluminum removing process: adding a sodium hydroxide pH regulator into the crude ferrous sulfate solution under stirring, regulating the pH of the solution to 5.0, completely converting trivalent aluminum ions in the solution into aluminum hydroxide precipitate, continuously stirring for 20min after regulating the pH, and filtering to obtain a solution after aluminum removal; wherein the reaction temperature is normal temperature, and the stirring intensity is 300 rpm. The impurity element analysis of the solution after the removal of aluminum is shown in the following table 3:
TABLE 3
As can be seen from the comparison between tables 3 and 2, the aluminum content in the solution is greatly reduced through the aluminum removal process.
And thirdly, heavy metal removing process. Adding a sodium sulfide heavy metal trapping agent into the solution after aluminum removal for reaction for 40min at 40 ℃ under stirring, and then filtering to obtain a pure ferrous sulfate solution; wherein the stirring speed is controlled to be 400rpm, and the adding amount of the sodium sulfide heavy metal catching agent is controlled to be 0.5 g/L. The analysis of the impurity elements in the ferrous sulfate solution is shown in table 4 below:
TABLE 4
As can be seen from comparison of tables 4 and 3, the content of each impurity element is further reduced through the heavy metal removal process.
Adjusting the iron concentration. Adding pure water into the ferrous sulfate solution for dilution, and controlling the concentration of ferrous sulfate in the solution to be 200g/kg to obtain a ferrous sulfate reaction solution for later use.
(3) Synthesizing iron phosphate:
adding sodium hydroxide into industrial phosphoric acid, and adjusting the pH value of the solution to 7.0, wherein the oxidant is 20 wt% of hydrogen peroxide, and the addition amount of the hydrogen peroxide is 1.18 times of the reaction amount; adding hydrogen peroxide into a phosphorus salt solution with the pH value of 7.0, and uniformly mixing to obtain a reaction phosphorus salt solution for later use.
During synthesis, the reaction is controlled by the formula (n), (P): and (n), (Fe): 1.02:1, dropwise adding the prepared reaction phosphate solution into the ferrous sulfate solution by taking the ferrous sulfate reaction solution as a base solution, heating to 94 ℃ after dropwise adding, reacting for 2 hours, filtering to obtain an iron phosphate filter cake, and washing, drying and calcining the iron phosphate filter cake to obtain the battery-grade anhydrous iron phosphate.
Examples 2 to 3
These examples are provided to illustrate the method of the present invention for producing battery grade iron phosphate from pyrite cinder.
The same procedure as in example 1 was used to prepare battery grade anhydrous iron phosphate, except that the specific conditions of step (1) in the examples are shown in table 5 below.
TABLE 5
Comparative example 1
Battery grade anhydrous iron phosphate was prepared in the same manner as in example 1, except that the cosolvent EDTA was replaced with the existing cosolvent sodium hexametaphosphate.
Comparative example 2
Battery grade anhydrous iron phosphate was prepared in the same manner as in example 1, except that the amount of EDTA added as a cosolvent was changed from 3% to 1% of the mass of the pyrite cinder.
Comparative example 3
Battery grade anhydrous iron phosphate was prepared in the same manner as in example 1, except that the amount of EDTA added as a cosolvent was changed from 3% to 10% of the mass of the pyrite cinder.
The leaching rates of iron in examples 1 to 3 and comparative examples 1 to 3 were measured, respectively, and the results are shown in table 6 below.
TABLE 6
Numbering
|
Leaching rate of iron (%)
|
Example 1
|
90.83
|
Example 2
|
96.77
|
Example 3
|
94.12
|
Comparative example 1
|
78.81
|
Comparative example 2
|
73.54
|
Comparative example 3
|
92.34 |
As can be seen from the results in table 6, the leaching rate of iron was significantly improved in example 1 using the co-solvent EDTA, compared to comparative example 1 (comparative example 1 using the existing co-solvent sodium hexametaphosphate), and pyrite cinder could be more effectively utilized.
In addition, compared with the example 1, in the comparative examples 2 to 3, the range of the cosolvent EDTA is not in the preferable range of the cosolvent which is 3 to 8 percent of the quality of the pyrite cinder, namely, the amount of the cosolvent EDTA in the comparative example 2 is too small, and the leaching rate is lower; in the comparative example 3, the cosolvent EDTA is excessive, and the leaching rate is not obviously improved. Therefore, in the invention, the addition amount of the cosolvent EDTA is preferably 3-8% of the quality of the pyrite cinder, considering the comprehensive consideration of the leaching rate and the saving of the use amount of the EDTA.
Comparative example
In this comparative example, battery grade anhydrous iron phosphate was prepared using the same method as in step (3) in example 1, except that ferrous sulfate heptahydrate was used instead of the ferrous sulfate reaction solution prepared in steps (1) to (2) in example 1.
The prepared anhydrous iron phosphate was tested as follows.
The anhydrous iron phosphate products prepared in example 1 and the comparative example were tested, and the test results are shown in table 7.
TABLE 7
As can be seen from the results in table 7, acceptable battery grade iron phosphate products were obtained using the method provided by the present invention, i.e., the results of example 1, with the respective impurity levels approaching those of anhydrous iron phosphate prepared using ferrous sulfate heptahydrate as the iron source. The method provided by the invention adopts pyrite cinder as an iron source, can prepare the qualified iron source applicable to preparing the battery-grade iron phosphate through a simple acid leaching process and an impurity removal process, can obviously reduce the cost, and has simple process and easy industrialization.